Good Folk. A question re. interpretation of the Creepage and Clearance tables in IEC 1010-1. BS EN 61010-1 etc.
The Facts: 1. I have a cable terminated with a female connector that carries 15kV to a fixed device (an electron gun on a vacuum system in this case). This is rather similar to a screened aircraft Spark Plug lead. 2. The cable is screened, and the connector is all metal (grounded) with a ptfe piece inside which supports the female contact, and provides an insulating sleeve up the inside of he connector body to provide the necessary clearance and creepage path lengths for reliable operation. 3. The ptfe inner does not extend all the way along the inside of the connector case, leaving a few mm of uninsulated (grounded) metal. 4. It is possible to put the IEC1010 Annexe B Test Finger into the connector and to touch the live receptacle, but it is impossible to do this without grounding the Test Finger on the Connector case. The Question... Am I right in assuming that using the Test Finger to locate (IEC 1010 6.2.) and measure (IEC1010 6.3.) the voltage on the accessible part, then using the circuit in IEC 1010 Figure A.2. I will show that the actual volts measured will be zero, so under those conditions claim that the connector can be described as 'safe'? In reality, if someone was to put their finger into the connector and touch the HV contact, they would provide a current path to earth (the body of the connector) through their finger, and one that would effectively bypass conduction through their body to earth. The source impedance of the 15kV is approx 150Kohms. So, does providing an unavoidable earthed 'guard ring' at the access to the high voltage terminal provide protection such that the Creepage and Clearances required in IEC 1010-1 can be disregarded? What do you think folks, Reasonable? Sensible? Safe? or What? Your opinions are, as always, most valuable. Thanks Chris Dupres Consulting Engineer Surrey UK
